The present invention relates to an infinitely variable traction roller transmission for the transmission of power over a large transmission ratio range.
Infinitely variable transmissions have generally a relatively limited ratio range and a limited torque transmission capability. Partly as a result of this they are not used in connection with large cars or trucks. Trucks require a full power transmission load capability at very low speeds, for example, when climbing a mountain road since, for their large weight, they have relatively small engines of relatively low power output and yet, at long level road stretches, they reach high speeds. A large transmission ratio range is therefore needed to provide sufficient torque at the drive wheels at start up or during climbing and to avoid engine overspeed at high vehicle travel speeds.
It is also important that trucks operate efficiently, that is, at optimum engine speed independently of the vehicle speed. An infinitely variable transmission would therefore be most desirable. Unfortunately no rugged infinitely variable transmissions with large transmission ratio range are in existence.
Infinitely variable transmissions and more specifically infinitely variable traction roller transmissions are well known. Those with which the present invention is concerned are generally of the type as shown, for example, in applicant's U.S. Pat. No. 4,086,820 of May 2, 1978, or in applicant's U.S. Pat. No. 4,702,118. However, in order to accommodate the power as needed in connection with trucks, such transmissions would have to be large and heavy and they would require additional mechanical gear shift transmissions in order to achieve the needed transmission ratio ranges.
It is therefore the principal object of the present invention to provide an infinitely variable traction roller transmission which is relatively small but capable of handling the power for driving heavy trucks at low and high truck operating speeds at optimum engine speed.